The separation of diisopropyl ether from isopropyl alcohol and water has been a challenging separation due to the azeotropes that form. U.S. Pat. No. 5,154,801 describes a separation process designed to specifically avoid forming an isopropyl alcohol-water azeotrope during the effluent processing of a diisopropyl ether production process. Most of the time azeotropes do form and, historically, approaches to perform the separation have included adsorption, U.S. Pat. No. 5,057,629, solvent Extraction, U.S. Pat. No. 4,182,914, and distillation followed by decantation, U.S. Pat. No. 4,857,664. By far the most popular approach has been water washing, see U.S. Pat. No. 4,906,787, U.S. Pat. No. 5,208,387, U.S. Pat. No. 5,113,024, U.S. Pat. No. 5,504,257, U.S. Pat. No. 5,324,866, U.S. Pat. No. 5,371,301 and U.S. Pat. No. 5,600,023. Water washing, although effective and successful, has several drawbacks. The first involves the high quantity of water that must be maintained within the system to perform the washing. A water wash unit and more conduits become necessary and the size of some vessels is increased to accommodate the high quantity of water, all of which increases the cost of the system. Another drawback arises when the spent water is recycled back to a distillation column to regenerate wash water. Utility costs increase under the burden of continually reboiling a large quantity of water.
The present invention provides an alternative that advantageously uses the diisopropyl ether-isopropyl alcohol-water azeotrope to separate diisopropyl ether from a mixture of diisopropyl ether, isopropyl alcohol and water. The azeotrope is intentionally formed and first used to draw substantially all of the diisopropyl ether present in a mixture into an overhead stream of a distillation column. The overhead stream is condensed and an aqueous phase and an organic phase are formed. The organic phase is passed to a drier column, while the aqueous phase is recycled to the distillation column. In the drier column, the diisopropyl ether-isopropyl alcohol-water azeotrope is again intentionally formed and now used to draw substantially all of the water and isopropyl alcohol into a drier overhead stream. Since isopropyl alcohol and water were removed in the aqueous phase of the previous column, it is now possible to form the desired bottoms diisopropyl ether product stream containing virtually no water or isopropyl alcohol. Using the present invention achieves the desired separation while also eliminating the need for a water wash unit and additional conduits, and lowering the utility cost by eliminating the need to reboil a large quantity of spent wash water.